1. Field of the Invention
The invention generally relates to a lens, and more particularly to a zoom lens.
2. Description of Related Art
With the advances in optical-electronic technologies, image sensing devices (such as a projector, a digital video camera (DVC) and a digital camera have been widely applied in daily life as well as in various industries, so as to replace tasks originally being done by human eye. In the image sensing device, besides qualities of an image sensor (e.g., a charge coupled device (CCD) and a complementary metal oxide semiconductor sensor (CMOS sensor)), a quality of an image being detected can also be decided by a quality of an optical lens. Therefore, how to design a lens to accomplish a preferable image is a major issue highly concerned by lens designers.
In order to achieve effects including wide angle, high zoom magnification, low distortion and higher image quality, a conventional zoom lens adopts a method of a multi-group operation for zooming. However, the zoom lens with the multi-group operation requires use of plural optical elements and mechanical members. If the zoom lens contains too many structural members, an optical length of the zoom lens cannot be reduced, and a price thereof cannot be reduced either. On the other hand, when a number of the mechanical members assembled in the zoom lens are reduced, flexibility in an optical design is limited. Accordingly, a difficulty in the optical design becomes higher. Therefore, how to reduce production costs while maintaining an image quality of the zoom lens has become one of the most important topics to be discussed in the field.
U.S. Pat. Nos. 8,159,758, 8,254,036, 7,933,073, 8,305,693, 5,710,669, 6,989,940, 7,440,194, 5,325,236, 5,864,435, and US patent publication number 20120268831 all provide a zoom lens.